Defective pixel specifying method, defective pixel specifying system, image correcting method, and image correcting system

ABSTRACT

A defective pixel specifying method and a defective pixel specifying system for a semiconductor device having a defective pixel are provided. Also provided are an image correcting method and an image correcting system for making a defective pixel inconspicuous on the screen when a read image is displayed. The present invention determines whether or not there is a defective pixel for each pixel and specifies the coordinate of the defective pixel using image signals obtained by reading a plurality of images. The image signal of the defective pixel is set based on the image signals of the pixels adjacent to the defective pixel to correct the image of the subject read.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a defective pixel specifying method anda defective pixel specifying system for a semiconductor device having animage sensor function. The present invention also relates to an imagecorrecting method and an image correcting system for an image read by asemiconductor device having an image sensor function.

2. Description of the Related Art

Various kinds of sensors are developed and put into practiceaccompanying technology advancement of late. These sensors are usedmainly to convert text and image information on paper into data forpersonal computers. Most of those sensors are semiconductor deviceshaving an image sensor function.

Examples of the above semiconductor devices include digital stillcameras, scanners, and copying machines. Digital still cameras are usedas replacements for conventional silver film cameras, and have areasensors in which pixels are arranged two-dimensionally. Scanners andcopying machines are used as means for reading text and imageinformation on paper, and have line sensors in which pixels are arrangedone-dimensionally.

Scanners can be roughly divided by their reading methods into threetypes; (1) sheet feeding type, (2) flat bed type, and (3) pen type(handy type). The sheet feeding type fixes an image sensor unit of ascanner and the original is moved along by a sheet feeder to read theoriginal. The flat bed type fixes the original on glass and an imagesensor unit is moved under the glass to read the original. The pen type(handy type) reads the original when a user moves an image sensor uniton the original.

Scanners of the above three types all employ optical systems. Flat bedtype scanners read images finely and therefore often employdemagnification optical systems. A lens used in a demagnificationoptical system has a long focal distance and, therefore, the distancebetween a subject and an image sensor unit is large, resulting in alarge-sized semiconductor device.

In order to make sheet feeding type and pen type (handy type) scannersportable, the devices have to be small in size. Accordingly,nonmagnification optical systems are employed in many cases. Anonmagnification optical system has a rod lens array interposed betweenan image sensor unit and a subject. The rod lens array is a bunch ofplural rod lenses having a distributed index of refraction. The rod lensarray forms an image at 1:1 and therefore has a short focal distance tomake the distance between the image sensor and a subject small.

Manufacturers of scanners recommend purchasers of their products toconduct calibration before starting reading a subject.

Calibration is recommended for the following two reasons.

Firstly, a subject is not irradiated uniformly with light from a lightsource in a scanner. As described above, a lens such as ademagnification optical system or a rod lens array is used in a scanner.Light from the light source provided in the scanner irradiates a subjectthrough those lenses. Accordingly, the intensity of light thatirradiates a subject may vary between different areas of the subject.

Secondly, fluctuation in characteristic between pixels of the imagesensor can be corrected by calibration. The fluctuation corresponds to aslight difference in signal value read by pixels when the scanner readsa subject that has identical information all over its surface. Thefluctuation between pixels causes a difference in signal value outputtedfrom a photoelectric conversion element even when light from the lightsource irradiates the subject at the same intensity. In most cases, thefluctuation in characteristic between pixels does not change with time.

Thus, calibration on a purchased scanner before starting reading asubject is recommended. In fact, some of scanners on the market containin their packages calibration sheets having the same sizes as theireffective reading range. Calibration sheets are white plastic sheets.Preferably, calibration sheets are untransmissive, solid and plasticsheets. It is also preferable for calibration sheets to have flatsurfaces with no hole or dent.

After a calibration sheet is read, all pixels should read identicalinformation. However, information actually read may vary from the tworeasons given in the above. Therefore, information when the white sheetis read is stored in a program in the scanner or other devices or media.Then, each time a subject is read, correction is made based on thestored information. Once calibration is conducted, the information isstored in a memory or the like and it is not necessary to repeatcalibration.

The method of calibration differs from one semiconductor device toanother. For instance, a scanner uses a calibration sheet forcalibration. A digital still camera is sold with calibration softwareincluded in the package. Then, calibration is conducted using thesoftware. With a digital still camera, a picture is taken through a lensand sometimes the image is slightly distorted. Distortion is measuredthrough calibration. A correction value for distortion of the lens iscalculated and inputted to a program of the digital still camera toreduce the influence of the distortion as much as possible.

A semiconductor device having an image sensor function is provided witha pixel portion that has a plurality of pixels. Each of the pixels has aphotoelectric conversion element and one or more transistors forcontrolling the photoelectric conversion element.

Semiconductor devices having an image sensor function are roughlydivided into CCD type and CMOS type. CMOS type semiconductor devices arefurther classified into passive semiconductor devices to whichamplifying transistors are not mounted and active semiconductor devicesto which amplifying transistors are mounted. An amplifying transistorhas a function of amplifying an image signal of a subject read by aphotoelectric conversion element.

An active semiconductor device has, in addition to an amplifyingtransistor as the one described above, semiconductor elements such as asensor selecting transistor. Accordingly, the number of elements in onepixel is large. When elements in one pixel are increased in number, theyield in manufacturing the semiconductor device lowers.

As a result, it is very difficult to obtain a semiconductor devicehaving no defective pixel. When forming a semiconductor device, asemiconductor device sometimes fails to form a photoelectric conversionelement in a pixel, or one of plural transistors for controlling thephotoelectric conversion element, properly. A pixel having a failedelement cannot operate normally and therefore is incapable of readingthe image of a subject correctly. When a semiconductor device having adefective pixel displays an image of a subject read, the defective pixelis often shown as a white dot or a black dot on the screen. Thus thedefective pixel on the screen is very noticeable and keeps thesemiconductor device from displaying the accurate image of the subjectread.

SUMMARY OF THE INVENTION

The present invention has been made in view of the problems above, andan object of the present invention is therefore to provide a defectivepixel specifying method and a defective pixel specifying system for asemiconductor device having a defective pixel. Another object of thepresent invention is to provide an image correcting method and an imagecorrecting system for making a defective pixel inconspicuous on thescreen when a read image is displayed.

The present invention employs the following measures to attain the aboveobjects. Now, a brief description is given on the present invention withreference to FIGS. 1A to 1D.

FIG. 1A shows an example in which an image of a subject in a uniformmiddle tone is read by a semiconductor device with pixels each includinga photoelectric conversion element and is displayed in a display unit206 (pixel portion 206) of an arbitrarily-chosen display device 207.FIG. 1B is an enlarged view of the area surrounded by bold lines forminga rectangle in FIG. 1A. FIG. 1B shows a pixel (m, n), pixels (m±1, n),pixels (m±1, n±1), and pixels (m, n±1). Numbers in the rectangles eachrepresenting a pixel represent image signals. As shown in FIG. 1B, imagesignals of pixels adjacent to the pixel (m, n) are all 200 whereas theimage signal of the pixel (m, n) itself is 55. The pixel (m, n) istherefore a defective pixel 101, and does not read information of asubject correctly.

Then, the defective pixel specifying method and image correcting methodof the present invention are applied to this device. The defective pixelspecifying method of the present invention is a defective pixelspecifying method characterized by comprising:

a first step of using a photoelectric conversion element to obtainplural image signals for each of pixels;

a second step of calculating for each of the pixels a first differenceor first ratio of the plural image signals obtained in the first step;

a third step of obtaining any one of the modal value, the average value,and the maximum value, of the first difference or first ratio in thepixel portion; and

a fourth step of obtaining for each of the pixels a second difference orsecond ratio to specify a defective pixel, the second difference orsecond ratio being the difference or ratio between one of the firstdifference and the first ratio and any one of the modal value, averagevalue, and maximum value obtained in the third step.

The image correcting method of the present invention is characterized bycomprising:

a first step of inputting image signals read by a photoelectricconversion element;

a second step of obtaining the average value of image signals of pixelsadjacent to a defective pixel;

a third step of setting the average value as an image signal of thedefective pixel; and

a fourth step of outputting the image signal of the defective pixel to adisplay device for displaying an image read by the photoelectricconversion element.

FIG. 1C shows a case in which an image of a subject is read by asemiconductor device that has the defective pixel specifying system andimage correcting system of the present invention. As shown in FIG. 1D,the image signal of the pixel (m, n) is set based on the image signalsof the pixels adjacent to the defective pixel. To elaborate, the imagesignal of the pixel (m, n) is changed from the initial 55 to 200. Thiscorrection makes the defective pixel 101 less conspicuous than in FIG.1A.

Thus, a defective pixel can be made inconspicuous in a semiconductordevice having a defective pixel by employing the present invention. Thedefective pixel seems as if it is repaired.

The present invention is effective for every semiconductor device thathas an image sensor function. For example, the present invention iseffective for CCD or CMOS type semiconductor devices having an imagesensor function, and for any other types of semiconductor devices havingan image sensor function as well. The present invention can workeffectively in a line sensor and an area sensor. A semiconductor devicefor reading a monochromatic image and a semiconductor device for readinga color image both can employ the present invention effectively. Thepresent invention is also effective for a semiconductor device formed ona single crystal (SOI or bulk) substrate and a semiconductor devicehaving a thin film transistor.

The present invention can use all kinds of photoelectric conversionelements. A photoelectric conversion element often used is a PNphotodiode. Also used are a PIN photodiode, an avalanche diode, an npnembedded diode, a Schottky diode, a phototransistor, an x-rayphotoconductor, and an infrared sensor.

The present invention is also effective for a semiconductor device inwhich a pixel is composed of a photoelectric conversion element having areading function and a display element for displaying an image read bythe photoelectric conversion element. In this semiconductor device, thepresent invention is used when information of a subject read isdisplayed by the display element and makes it seem as if a defectivepixel is repaired.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1D are diagrams illustrating the present invention:

FIGS. 2A to 2D are schematic diagrams showing the concept of the presentinvention;

FIGS. 3A to 3C are schematic diagrams showing the concept of the presentinvention;

FIG. 4 is a schematic diagram showing the concept of the presentinvention;

FIG. 5 is a circuit diagram of a semiconductor device to which thepresent invention can be applied;

FIG. 6 is a circuit diagram of a semiconductor device to which thepresent invention can be applied;

FIG. 7 is a circuit diagram of a semiconductor device to which thepresent invention can be applied;

FIG. 8 is a circuit diagram of a pixel in a semiconductor device towhich the present invention can be applied;

FIG. 9 is a diagram showing a mode of use of the present invention;

FIG. 10 is a diagram showing a mode of use of the present invention;

FIG. 11 is a diagram showing a mode of use of the present invention;

FIG. 12 is a diagram showing a mode of use of the present invention;

FIG. 13 is a diagram showing a mode of use of the present invention;

FIGS. 14A to 14D are diagrams of electronic equipment to which thepresent invention can be applied;

FIGS. 15A to 15C are diagrams of electronic equipment to which thepresent invention can be applied;

FIG. 16 is a circuit diagram of a pixel in a semiconductor device towhich the present invention can be applied;

FIG. 17 is a circuit diagram of a pixel in a semiconductor device towhich the present invention can be applied;

FIG. 18 is a diagram showing an operation mode of a semiconductor deviceto which the present invention can be applied; and

FIG. 19 is a diagram showing an operation mode of a semiconductor deviceto which the present invention can be applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode 1

This embodiment mode describes means for determining whether there is adefective pixel and means for specifying the coordinate of the defectivepixel in a defective pixel specifying method of the present invention.The description is given with reference to the flowchart of FIG. 2.

First, whether or not a pixel portion of a semiconductor device has adefective pixel is determined. The pixel portion reads at least twocalibration sheets of different colors to decide. In general, a color isdefined by three components; hue (corresponding to the wavelength of asingle color light), chroma (vividness, namely, how small the proportionof white is), and brightness (the intensity of light). In thisspecification, a color may have merely one component orarbitrarily-selected two components out of the above three components.Step 1 of this embodiment consists of reading a white calibration sheetand Step 2 consists of reading a black calibration sheet. Step 3involves obtaining the difference between image signal values obtainedin Steps 1 and 2.

To simplify the explanation, a 5×5 pixel portion 103 is shown in FIGS.2A to 2C to receive Steps 1 through 3. A pixel 102 is represented by asquare and a number in each square represents its image signal. Numbersaround the pixel portion 103 indicate coordinates of the pixels. FIG. 2Ashows image signals of the respective pixels after the white calibrationsheet is read. FIG. 2B shows image signals of the respective pixelsafter the black calibration sheet is read. An image signal valueobtained in Step 1 is denoted by S1 (m, n). (m, n) represents acoordinate and, for example, S1(1, 1) corresponds to 245. An imagesignal value obtained in Step 2 is denoted by S2 (m, n). For example,S2(1, 1) corresponds to 50. In this embodiment mode, m and n bothrepresent integers and respectively satisfy 1≦m≦5 and 1≦n≦5.

The white calibration sheet is used in Step 1 and the black calibrationsheet is used in Step 2 in this embodiment mode. This is because alarger difference obtained is preferred in order to determine whether ornot there is a defective pixel from the difference between an imagesignal value obtained in Step 1 and an image signal value obtained inStep 2. However, the present invention can use calibration sheets of anycolors other than a white calibration sheet and a black calibrationsheet as long as the sheets can produce a difference between an imagesignal value obtained in calibration of Step 1 and an image signal valueobtained in calibration of Step 2 in the same pixel.

Although this embodiment mode reads two calibration sheets to determinewhether there is a defective pixel, the number of calibration sheets isnot limited to two. It is sufficient in the present invention if thepresence or absence of a defective pixel is determined by reading atleast two calibration sheets of different colors. However, when morethan two calibration sheets are to be read, the difference between imagesignals is obtained for every set of two calibration sheets out of theplural calibration sheets. The difference values obtained are used tospecify a defective pixel.

In Step 3, the difference between the image signal value obtained inStep 1 for each pixel and the image signal value obtained in Step 2 foreach pixel is calculated. A number in a square representing one pixel102 in FIG. 2C represents the difference calculated. The differencebetween an image signal value in Step 1 and an image signal value inStep 2 in the same pixel is expressed as S3(m, n). For example, S3(1, 1)corresponds to 195.

Step 4 is for obtaining the average value of differences between imagesignals of the respective pixels. First, S3(m, n) values of the pixelsin the pixel portion 103 are summed up, and the obtained sum is dividedby the number of pixels (25, in this embodiment mode). The average valueobtained in Step 4 is expressed as S4(Ave). S4(Ave) is 193.8 for thepixel portion 103 shown in FIGS. 2A to 2C.

In Step 5, a S3(m, n) value of each pixel is compared with the S4(Ave)value, 193.8, obtained in Step 4. As shown in the following Expression1, a pixel having a S3(m, n) value that falls within 80 to 120% of theS4(Ave) value, 193.8, is deemed as a pixel with no defect. As shown inthe following Expressions 2 and 3, a pixel having S3(m, n) value that islower than 80% or higher than 120% of the average value of 193.8 isdeemed as a defective pixel.

Expression 1

0.8≦{S3(m,n)}/{S4(Ave)}≦1.2  (1)

Expression 2

0.8>{S3(m,n)}/{S4(Ave)}  (2)

Expression 3

1.2<{S3(m,n)}/{S4(Ave)}  (3)

In the pixel portion 103 shown in FIGS. 2A to 2C, the pixel (2, 3) isjudged as a defective pixel. Simultaneously, the coordinate of thedefective pixel, the pixel (2, 3), is stored in a defective pixelcoordinate memory.

The difference between an image signal value in Step 1 and an imagesignal value in Step 2 is obtained for each pixel in Step 3 in thisembodiment mode. However, the present invention is not limited thereto.For example, the sum of an image signal value in Step 1 and an imagesignal value in Step 2 may be obtained for each pixel in Step 3.Alternatively, the ratio or product of image signals in Steps 1 and 2may be obtained for each pixel in Step 3.

Although the average value is calculated in Step 4, the presentinvention is not limited thereto. In Step 4, the maximum value may beobtained instead, or the modal value may be obtained on the histogram. Auser may input a S4(Ave) value manually.

A pixel having a S3(m, n) value that falls within 80 to 120% of theS4(Ave) value is deemed as a pixel with no defect in Step 5 in thisembodiment mode. However, the present invention is not limited thereto.A user can suitably determine how large a difference between the S3(m,n) value and the value obtained in Step 4 should be for a pixel to bedeemed as a defective pixel. A defective pixel may be determined by aknown statistical method using variance or standard deviation.

Preferably, calibration that is a measure to specify the coordinate of adefective pixel is conducted when the semiconductor device is used forthe first time. Once the coordinate of a defective pixel is specified,the coordinate is stored in a defective pixel coordinate memory of thesemiconductor device. Therefore, it is unnecessary to repeatcalibration. If the coordinate of a defective pixel is already stored inthe defective pixel coordinate memory, calibration is omitted and theprocess is started with reading an image of a subject at the point A inthe flowcharts of FIGS. 2 and 3A.

Using the method described above, the present invention can readilydetermine whether there is a defective pixel and specify the coordinateof the defective pixel.

Embodiment Mode 2

This embodiment mode describes means for setting an image signal of adefective pixel in an image correcting method of the present invention.The description is given with reference to FIGS. 3A to 3C.

As shown in FIG. 3A, after the coordinate of a defective pixel 101 isspecified and is stored in a defective pixel coordinate memory, an imagesignal of the defective pixel 101 is set based on image signals ofpixels adjacent to the defective pixel.

FIG. 3B shows a case in which a semiconductor device reads informationof a subject in monochrome and displays a monochromatic image of thesubject. If the coordinate of the defective pixel 101 is given as (m,n), pixels adjacent to the defective pixel 101 are pixels (m, n±1),pixels (m±1, n±1), and pixels (m±1, n), which are eight pixels in total.An image signal of the defective pixel is set based on image signals ofthese eight adjacent pixels. To elaborate, the average value of imagesignals of the pixels (m, n±1), pixels (m±1, n±1), and pixels (m±1, n)adjacent to the defective pixel 101 is obtained and set as an imagesignal of the defective pixel 101.

In FIG. 3B, the image signal of the defective pixel 101(m, n) is setbased on the image signals of the pixels (m, n±1), pixels (m±1, n±1),and pixels (m±1, n), eight pixels in total. However, the presentinvention is not limited thereto. For instance, pixels (m±2, n±2) may beadded to the above eight pixels to obtain the average value of imagesignals of twelve pixels in total. Alternatively, the average value oftwo pixels (m±1, n) to the right and left of the defective pixel 101, orthe average value of two pixels (m, n±1) above and below the defectivepixel 101, may be used. The defective pixel 101 may be set to have thesame image signal as any one of the eight pixels (m, n±1), (m±1, n±1),and (m±1, n) adjacent to the defective pixel 101. In short, a user canappropriately choose pixels from those adjacent to a defective pixel touse the average value of image signals of the chosen pixels as an imagesignal of the defective pixel.

When a defective pixel is located at an end of pixel matrix, an imagesignal of the defective pixel may be set based only on an image signalof one adjacent pixel. If a semiconductor device has a first defectivepixel and a second defective pixel next to each other, an image signalof the first defective pixel may be set based on image signals of pixelsadjacent to the first defective pixel except the second defective pixel.

FIG. 3C shows a case in which a semiconductor device reads informationof a subject in color and displays a color image of the subject. Roughlyspeaking, there are two methods of reading an image of a subject incolor. One method includes providing a photoelectric conversion elementin every pixel and switching light sources for red (R), green (G), andblue (B) three times to read a subject three times.

The other method includes providing three photoelectric conversionelements in every pixel, providing the device with red (R), green (G),and blue (B) color filters, and reading a subject once with light from awhite light source. This method is further divided into a case in whichone color filter is provided in one pixel and information of othercolors are supplied from the adjacent pixels, and a case in which onepixel is divided into three sub-pixels and red (R), green (G), and blue(B) color filters are respectively provided in the sub-pixels. Thesecond case of the latter method is described in this embodiment mode.

Reference numeral 102 denotes a pixel, which has a sub-pixel R (m−1,n−1), a sub-pixel G (m−1, n−1), and a sub-pixel B (m−1, n−1). If thecoordinate of a defective sub-pixel 301 is given as (m, n), sub-pixelssurrounding the defective sub-pixels are sub-pixels G (m, n±1),sub-pixels G (m±1, n±1), and sub-pixels G (m±1, n), eight sub-pixels intotal. An image signal of the defective sub-pixel 301 is set based onimage signals of these eight adjacent sub-pixels. To elaborate, theaverage value of image signals of the sub-pixels G (m, n±1), sub-pixelsG (m±1, n±1), and sub-pixels G (m±1, n) surrounding the defectivesub-pixel 301 is obtained and set as an image signal of the defectivesub-pixel 301.

In FIG. 3C, the image signal of the defective sub-pixel 301 (m, n) isset based on the image signals of the sub-pixels G (m, n±1), sub-pixelsG (m±1, n±1), and sub-pixels G (m±1, n), eight sub-pixels in total.However, the present invention is not limited thereto. For instance,sub-pixels G (m±2, n±2) may be added to the above eight sub-pixels toobtain the average value of image signals of twelve sub-pixels in total.Alternatively, the average value of two sub-pixels G (m±1, n) may beused. In short, a user can appropriately choose sub-pixels from thoseadjacent to a defective sub-pixel to use the average value of imagesignals of the chosen sub-pixels as an image signal of the defectivesub-pixel. Correction of an image of a subject using the presentinvention may be made after data of the subject corresponding to theentire screen are read. Alternatively, an image of a subject may becorrected each time reading one row or one pixel of information of thesubject is completed.

Using the method described above, the present invention can readily setan image signal of a defective pixel. As a result, the defective pixelseems as if it is repaired.

This embodiment mode may be combined freely with Embodiment Mode 1.

Embodiment Mode 3

This embodiment mode describes the relation between a pixel portion witha plurality of pixels each having a photoelectric conversion element anda display device for displaying an image of a subject read by the pixelportion. The description is given with reference to FIG. 4.

In FIG. 4, a pixel portion 200 is provided with a photoelectricconversion element having a reading function. Information of a subjectread by the pixel portion 200 is outputted to a defective pixelrepairing system. In this embodiment mode, a defective pixel specifyingsystem and an image correcting system are collectively called adefective pixel repairing system.

The defective pixel repairing system has a CPU 202, an image signalrepairing circuit 203, and a defective pixel coordinate memory 204. Thedefective pixel repairing system of the present invention has means fordetermining whether there is a defective pixel in the pixel portionthrough calibration and for specifying the coordinate of the defectivepixel. The system is also characterized by having means for setting animage signal of the defective pixel based on image signals of pixelsadjacent to the defective pixel.

Once the coordinate of a defective pixel is specified, the defectivepixel coordinate memory 204 stores the coordinate of the defectivepixel. The image signal repairing circuit 203 sets an image signal ofthe defective pixel based on image signals of pixels adjacent to thedefective pixel. To elaborate, the average value of image signals ofpixels adjacent to the defective pixel is obtained to set the averagevalue as an image signal of the defective pixel.

A control circuit 205 outputs the image signal of the defective pixelwhich is set by the defective pixel repairing system, and image signalsof other pixels than the defective pixel to a display unit 206. Thedisplay unit 206 displays the image of the subject read by the pixelportion 200.

The present invention is effective for every semiconductor device thathas an image sensor function. For example, the present invention iseffective for CCD or CMOS type semiconductor devices having an imagesensor function, and for any other types of semiconductor devices havingan image sensor function as well. The present invention can workeffectively in a line sensor and an area sensor. A semiconductor devicefor reading a monochromatic image and a semiconductor device for readinga color image both can employ the present invention effectively. Thepresent invention is also effective for a semiconductor device formed ona single crystal (SOI or bulk) substrate and a semiconductor devicehaving a thin film transistor.

In the case of a semiconductor device having a reading function alone,such as a scanner, the present invention is employed to display an imagewith an arbitrarily-chosen display device while making a defective pixelseem as if it is repaired. When information of a subject read by ascanner is to be displayed with an arbitrarily-chosen display device,the pixel portion 200 and the display unit 206 shown in FIG. 4 areseparate devices.

In a semiconductor device in which one pixel is composed of aphotoelectric conversion element and a light emitting element, the samepixel conducts both reading information of a subject and displaying thesubject. In a semiconductor device as this, the pixel portion 200 andthe display unit 206 shown in FIG. 4 are one device.

This embodiment mode may be combined freely with Embodiment Modes 1 and2.

Embodiment 1

This embodiment describes an example of a semiconductor device to whichthe present invention can be applied.

FIG. 5 is a circuit diagram of a pixel portion in a passivesemiconductor device. A pixel portion 103 has sensor selecting signallines (SG1 to SGy) and sensor signal output lines (SS1 to SSx).

The pixel portion 103 has a plurality of pixels 102. Each of the pixels102 has a photodiode 111, a sensor selecting transistor 112, one of thesensor selecting signal lines (SG1 to SGy), and one of the sensor signaloutput lines (SS1 to SSx).

A P channel side terminal of the photodiode 111 is connected to a powersupply reference line 121. The sensor selecting transistor 112 has asource region and a drain region one of which is connected to an Nchannel side terminal of the photodiode 111 and the other of which isconnected to the sensor signal output line (one of SS1 to SSx). A gateelectrode of the sensor selecting transistor 112 is connected to thesensor selecting signal line (one of SG1 to SGy).

When the pixel portion 103 of the semiconductor device shown in FIG. 5has a defective pixel, the present invention is applied to make thedefective pixel seem as if it is repaired.

This embodiment may be combined freely with Embodiment Modes 1 through3.

Embodiment 2

This embodiment describes a semiconductor device different from the onein Embodiment 1.

FIG. 6 is a Circuit diagram of a pixel portion in an activesemiconductor device. A pixel portion 103 has sensor selecting signallines (SG1 to SGv), sensor resetting signal lines (SR1 to SRy), sensorsignal output lines (SS1 to SSx), and sensor power supply lines (VB1 toVBx).

The pixel portion 103 has a plurality of pixels 102. Each of the pixels102 has a photodiode 111, a sensor selecting transistor 112, anamplifying transistor 113, a sensor resetting transistor 114, one of thesensor selecting signal lines (SG1 to SGy), one of the sensor resettingsignal lines (SR1 to SRy), one of the sensor signal output lines (SS1 toSSx), and one of the sensor power supply lines (VB1 to VBx).

A P channel side terminal of the photodiode 111 is connected to a powersupply reference line 121. An N channel side terminal of the photodiode111 is connected to a gate electrode of the amplifying transistor 113.

The amplifying transistor 113 has a drain region and a source region oneof which is connected to the sensor power supply line (one of VB1 toVBx) and the other of which is connected to a drain region of the sensorselecting transistor 112. The amplifying transistor 113 and a biastransistor 120 together make a source follower circuit. Accordingly, itis desirable for the amplifying transistor 113 and the bias transistor120 to have the same polarity.

A gate electrode of the sensor selecting transistor 112 is connected tothe sensor selecting signal line (one of SG1 to SGy). A source region ofthe sensor selecting transistor 112 is connected to the sensor signaloutput line (one of SS1 to SSx).

A gate electrode of the sensor resetting transistor 114 is connected tothe sensor resetting signal line (one of SR1 to SRy). The sensorresetting transistor 114 has a source region and a drain region one ofwhich is connected to the sensor power supply line (one of VB1 to VBx)and the other of which is connected to the gate electrode of theamplifying transistor 113.

The bias transistor 120 has a source region and a drain region one ofwhich is connected to the sensor signal output line (one of SS1 to SSx)and the other of which is connected to a power supply line 122. A gateelectrode of the bias transistor 120 is connected to a bias signal line(BS).

When the pixel portion 103 of the semiconductor device shown in FIG. 6has a defective pixel, the present invention is applied to make thedefective pixel seem as if it is repaired.

The descriptions given in Embodiments 1 and 2 are about CMOS typesemiconductor devices. However, the present invention is also applicableto CCD type semiconductor devices. This embodiment may be combinedfreely with Embodiment Modes 1 through 3 and Embodiment 1.

Embodiment 3

This embodiment describes an example different from the ones inEmbodiments 1 and 2. A semiconductor device described in this embodimenthas a light emitting element and a photoelectric conversion element inone pixel. The description is given with reference to FIGS. 7 and 8.

A pixel portion 103 has source signal lines (S1 to Sx), power supplyinglines (V1 to Vx), selecting signal lines (EG1 to EGy), resetting signallines (ER1 to ERy), sensor selecting signal lines (SG1 to SGy), sensorresetting signal lines (SR1 to SRy), sensor signal output lines (SS1 toSSx), and sensor power supply lines (VB1 to VBx).

The pixel portion 103 has a plurality of pixels 102. Each of the pixels102 has one of the source signal lines (S1 to Sx), one of the powersupplying lines (V1 to Vx), one of the selecting signal lines (EG1 toEGy), one of the resetting signal lines (ER1 to ERy), one of the sensorselecting signal lines (SG1 to SGy), one of the sensor resetting signallines (SR1 to Sry) one of the sensor signal output lines (SS1 to SSx),and one of the sensor power supply lines (VB1 to VBx). Each of thepixels 102 also has a selecting transistor 116, a driving transistor119, a resetting transistor 117, a sensor selecting transistor 112, anamplifying transistor 113, and a sensor resetting transistor 114.

A bias transistor 120 has a source region and a drain region one ofwhich is connected to the sensor signal output line (one of SS1 to SSx)and the other of which is connected to a power supply line 122. A gateelectrode of the bias transistor 120 is connected to a bias signal line(BS).

FIG. 8 shows a pixel (i, j) located at Row i and Column j in the pixelportion of FIG. 7.

The photodiode 111 has an n-channel terminal, a p-channel terminal, anda photoelectric conversion layer that is placed between the n-channelterminal and the p-channel terminal. One of the n-channel terminal andthe p-channel terminal is connected to a power supply reference line 121and the other is connected to a gate electrode of the amplifyingtransistor 113.

A gate electrode of the sensor selecting transistor 112 is connected tothe sensor selecting signal line (SGj). The sensor selecting transistor112 has a source region and a drain region one of which is connected toa source region of the amplifying transistor 113 and the other of whichis connected to the sensor signal output line (SSi). The sensorselecting transistor 112 is a transistor functioning as a switchingelement when a signal of the photodiode 111 is outputted.

A drain region of the amplifying transistor 113 is connected to thesensor power supply line (VBi). The source region of the amplifyingtransistor 113 is connected to the source region or drain region of thesensor selecting transistor 112. The amplifying transistor 113 and thebias transistor 120 together make a source follower circuit.Accordingly, it is desirable for the amplifying transistor 113 and thebias transistor 120 to have the same polarity.

A gate electrode of the sensor resetting transistor 114 is connected tothe sensor resetting signal line (SRj). The sensor resetting transistor114 has a source region and a drain region one of which is connected tothe sensor power supply line (VBi) and the other of which is connectedto the photodiode 111 and to the gate electrode of the amplifyingtransistor 113. The sensor resetting transistor 114 is a transistorfunctioning as an element for initializing the photodiode 111.

A light emitting element 115 has an anode, a cathode, and an organiccompound layer that is placed between the anode and the cathode. Whenthe anode is connected to a source region or drain region of the drivingtransistor 119, the anode serves as a pixel electrode whereas thecathode serves as an opposite electrode. On the other hand, the cathodeserves as the pixel electrode and the anode serves as the oppositeelectrode when the cathode is connected to the source region or drainregion of the driving transistor 119.

A gate electrode of the selecting transistor 116 is connected to theselecting signal line (EGj). The selecting transistor 116 has a sourceregion and a drain region one of which is connected to the source signalline (S1) and the other of which is connected to a gate electrode of thedriving transistor 119. The selecting transistor 116 is a transistorfunctioning as a switching element when a signal is written in the pixel(i, j).

One of the source region and drain region of the driving transistor 119is connected to the power supplying line (Vi) and the other is connectedto the light emitting element 115. A capacitor 118 is connected to thegate electrode of the driving transistor 119 and to the power supplyingline (Vi). The driving transistor 119 is a transistor functioning as acurrent controlling element, namely, an element for controlling acurrent supplied to the light emitting element 115.

The resetting transistor 117 has a source region and a drain region oneof which is connected to the power supplying line (Vi) and the other ofwhich is connected to the gate electrode of the driving transistor 119.A gate electrode of the resetting transistor 117 is connected to theresetting signal line (ERj). The resetting transistor 117 is atransistor functioning as an element for erasing (resetting) a signalwritten in the pixel (i, j).

The semiconductor device of the present embodiment has a plurality oftransistors for controlling the photoelectric conversion element andtransistors for controlling the light emitting element. Information of asubject read by the photoelectric conversion element is displayed by thelight emitting element provided in the same pixel.

A defective pixel as defined in this specification is a pixel in which aphotoelectric conversion element having a reading function or atransistor for controlling the photoelectric conversion element has adefect. If such a pixel has a light emitting element and a transistorfor controlling the light emitting element that are not defective, thepresent invention can be applied to this pixel.

When the pixel portion 103 of the semiconductor device shown in FIG. 7has a defective pixel, the present invention is applied to make thedefective pixel seem as if it is repaired.

This embodiment may be combined freely with Embodiment Modes 1 through 3and Embodiments 1 and 2.

Embodiment 4

This embodiment gives a brief description on operation of the activeCMOS sensor semiconductor device described in Embodiment 2. FIG. 16shows a pixel (i, j) located at Row i and Column j in the pixel portion103 of FIG. 6.

In the pixel (i, j) shown in FIG. 16, first, the sensor resettingtransistor 114 is turned conductive. As the sensor resetting transistor114 is turned conductive, the p-channel terminal of the photoelectricconversion element 111 is connected to the power supply reference line121 and the n-channel terminal of the photoelectric conversion element111 is electrically connected to the sensor power supply line (VBi). Atthis point, the electric potential of the power supply reference line121 is at a reference electric potential 0 V and the electric potentialof the sensor power supply line (VBi) is at a power supply electricpotential Vdd. Accordingly, a reverse bias voltage is given to thephotoelectric conversion element 111. In this specification, a chargingoperation in which the electric potential of the n-channel terminal ofthe photoelectric conversion element 111 is raised to the level of theelectric potential of the sensor power supply line (VBi) is called areset operation.

Next, the sensor resetting transistor 114 is turned unconductive. Withthe sensor resetting transistor 114 being unconductive, thephotoelectric conversion element 111 generates electric charges throughphotoelectric conversion if the photoelectric conversion element 111 isirradiated with light. Therefore, the electric potential of then-channel terminal of the photoelectric conversion element 111, whichhas been raised to the level of the electric potential of the sensorpower supply line (VBi), is gradually lowered with time.

After allowing a certain period of time to pass, the sensor selectingtransistor 112 is turned conductive. As the sensor selecting transistor112 is turned conductive the electric potential of the n-channelterminal of the photoelectric conversion element 111 is outputted to thesensor signal output line (SSi) through the amplifying transistor 113.

However, while the electric potential of the n-channel terminal of thephotoelectric conversion element 111 is outputted to the sensor signaloutput line (SSi), an electric potential is given to the bias signalline (BS). That means a current is flowing in the bias transistor 120during this and therefore the amplifying transistor 113 and the biastransistor 120 are functioning as a source follower circuit.

The wiring line to which the p-channel terminal of the photoelectricconversion element 111 is connected in FIG. 16, namely, the power supplyreference line 121 may also be called a photoelectric conversion elementside power supply line. The electric potential of the photoelectricconversion element side power supply line changes depending on how thephotoelectric conversion element 111 is aligned. In FIG. 16, thephotoelectric conversion element side power supply line is connected tothe p-channel terminal of the photoelectric conversion element 111 andhas the reference electric potential 0 V. This is why the photoelectricconversion element side power supply line is called as a power supplyreference line in FIG. 16.

Similarly, the wiring line to which the sensor resetting transistor 114is connected in FIG. 16, namely, the sensor power supply line (VBi) mayalso be called a reset side power supply line. The electric potential ofthe reset side power supply line changes depending on how thephotoelectric conversion element 111 is aligned. In FIG. 16, the resetside power supply line is connected to the n-channel terminal of thephotoelectric conversion element 111 through the sensor resettingtransistor 114 and has the power supply electric potential Vdd. This iswhy the reset side power supply line is called as a power supply line inFIG. 16.

The operation of resetting the photoelectric conversion element 111 isidentical with the operation of giving the photoelectric conversionelement 111 a reverse bias voltage. Accordingly, which of thephotoelectric conversion element side power supply line and the resetside power supply line has a higher electric potential changes dependingon how the photoelectric conversion element 111 is aligned.

Next, an example of a basic source follower circuit is shown in FIG. 17and the operation thereof is described below. The example shown in FIG.17 uses n-channel transistors but p-channel transistors may be used toconstitute the source follower circuit.

An amplifier side power supply line 130 receives the power supplyelectric potential Vdd and the power supply line 122 receives thereference electric potential 0 V. The drain region of the amplifyingtransistor 113 is connected to the amplifier side power supply line 130and the source region of the amplifying transistor 113 is connected tothe drain region of the bias transistor 120. The source region of thebias transistor 120 is connected to the power supply line 122.

The gate electrode of the bias transistor 120 receives a bias electricpotential Vb and a bias current Ib flows in the bias transistor 120. Thebias transistor 120 operates as a constant current supply.

In FIG. 17, the gate electrode of the amplifying transistor 113 servesas an input terminal 131. Therefore an input electric potential Vin isapplied to the gate electrode of the amplifying transistor 113. Thesource region of the amplifying transistor 113 serves as an outputterminal 132. Therefore an output electric potential Vout is theelectric potential of the source region of the amplifying transistor113. The input/output electric potential of the source follower circuitsatisfies Vout=Vm−Vb.

In FIG. 17, it is assumed that the sensor selecting transistor 112 isconductive and the transistor 112 is omitted from the drawing. Theelectric potential of the n-channel terminal of the photoelectricconversion element 111 corresponds to the input electric potential Vin(the gate electric potential of the amplifying transistor 113, namely,the electric potential of the input terminal 131). The electricpotential of the sensor signal output line (SSi) corresponds to theoutput electric potential Vout (the source electric potential of theamplifying transistor 113, namely, the electric potential of the outputterminal 132). The sensor power supply line (VBi) corresponds to theamplifier side power supply line 130.

Accordingly, in FIG. 16, the electric potential of the n-channelterminal of the photoelectric conversion element 111 is Vpd, theelectric potential of the bias signal line (BS), namely, the biaselectric potential, is Vb, and the electric potential of the sensorsignal output line (SSi) is Vout. When the power supply reference line121 and the power supply line 122 have an electric potential of 0 V,Vout=Vpd−Vb. Therefore Vout changes as the electric potential Vpd of then-channel terminal of the photoelectric conversion element 111 changes,outputting as a signal the change in Vpd. This allows the photoelectricconversion element 111 to read intensity of light.

The description given next with reference to the timing chart of FIG. 18is about a selecting signal, a resetting signal, and a signal red by thephotoelectric conversion element in each of the pixels 102.

First, the sensor resetting signal line (one of SR1 to SRy) iscontrolled to turn the sensor resetting transistor 114 conductive.

Next, the n-channel terminal of the photoelectric conversion element 111is charged until its electric potential reaches the level of theelectric potential of the sensor power supply line (one of VB1 to VBx),namely, the power supply electric potential Vdd. In other words, thepixel is reset. Then the sensor resetting signal line (one of SR1 toSRy) is controlled to turn the sensor resetting transistor 114unconductive.

Thereafter the photoelectric conversion element 111 generates electriccharges in an amount according to the intensity of light if thephotoelectric conversion element 111 is irradiated with light. Theelectric charges charged by reset operation are gradually discharged tolower the electric potential of the n-channel terminal of thephotoelectric conversion element 111.

As shown in FIG. 18, when the photoelectric conversion element 111 isirradiated with bright light, a large amount of electric charges aredischarged to lower the electric potential of the n-channel terminal ofthe photoelectric conversion element 111. When the photoelectricconversion element 111 is irradiated with weak light, a small amount ofelectric charges are discharged and therefore the electric potential ofthe n-channel terminal of the photoelectric conversion element 111 islowered less than in the case where the element is irradiated withbright light.

Then at one point, the sensor selecting transistor 112 is turnedconductive to read as a signal the electric potential of the n-channelterminal of the photoelectric conversion element 111. The signal is inproportion to the intensity of light that irradiates the photoelectricconversion element 111. The sensor resetting transistor 114 is againturned conductive to reset the photoelectric conversion element 111 andrepeat the operations described above.

If the photoelectric conversion element 111 is irradiated with toobright light, a very large amount of electric charges thereof aredischarged to greatly lower the electric potential of the n-channelterminal of the photoelectric conversion element 111. However, theelectric potential of the n-channel terminal of the photoelectricconversion element 111 is never reduced to a level lower than theelectric potential of the p-channel terminal of the photoelectricconversion element 111, namely, the electric potential of the powersupply reference line 121.

When the electric potential of the n-channel terminal of thephotoelectric conversion element 111 is reduced due to irradiation ofvery bright light, the electric potential stops lowering once it reachesthe level of the electric potential of the power supply reference line121. This is called saturation. If it reaches the saturation, theelectric potential of the n-channel terminal of the photoelectricconversion element 111 no longer changes to make it impossible to outputa signal in accordance with the correct intensity of light. Therefore,for the sake of normal operation, the device has to be operated in themanner that prevents the photoelectric conversion element 111 fromreaching saturation.

A period started with reset of the pixel and ended with output of thesignal is called an accumulation time. The accumulation time refers to atime in which a light receiving unit of an image sensor is irradiatedwith light and signals are accumulated, and is also called an exposuretime. In the accumulation time, the photoelectric conversion element 111accumulates electric charges generated from light that irradiates thephotoelectric conversion element 111.

Accordingly, when the length of accumulation time differs, the totalamount of electric charges generated from light also differs to vary thesignal value even if the intensity of light is the same. For example, anintense light irradiating the photoelectric conversion element 111causes saturation in a short accumulation time. A weak light irradiatingthe photoelectric conversion element 111 can also cause saturation ifthe accumulation time is long enough. In other words, the signal valueis determined by the product of the intensity of light irradiating thephotoelectric conversion element 111 and the length of accumulationtime.

This embodiment may be combined freely with Embodiment Modes 1 through 3and Embodiments 1 through 3.

Embodiment 5

This embodiment describes with reference to FIGS. 18 and 19 the electricpotential of a photoelectric conversion element when reading a blackcalibration sheet. FIG. 18 is used to describe the electric potential ofa photoelectric conversion element in an active semiconductor device andthen FIG. 19 is used to describe the electric potential of aphotoelectric conversion element in a passive semiconductor device.

In this embodiment, a resetting signal is applied to a sensor resettingtransistor 114 in an active CMOS sensor semiconductor device. Describedhere is an operation of reading the electric potential of an n-channelterminal of a photoelectric conversion element 111 upon application ofthe resetting signal.

The electric potential of the n-channel terminal of the photoelectricconversion element 111 which is read upon application of the resettingsignal to the sensor resetting transistor 114 is almost the same as theelectric potential of the photoelectric conversion element 111 readafter a black calibration sheet is read. In other words, the operationof reading the electric potential of the n-channel terminal of thephotoelectric conversion element 111 upon application of the resettingsignal to the sensor resetting transistor 114 is equal to the operationof reading a black calibration sheet. The reason is given below.

When reading a black calibration sheet, the photoelectric conversionelement 111 is hardly irradiated with light. In other words,photoelectric conversion in the photoelectric conversion element 111hardly takes place and no electric charges are accumulated in thephotoelectric conversion element 111. Therefore, the electric potentialof the n-channel terminal of the photoelectric conversion element 111when reading a black calibration sheet has almost the same value as theelectric potential of the sensor power supply lines (VB1 to VBx).

On the other hand, when the resetting signal is applied to the sensorresetting transistor 114, the n-channel terminal of the photoelectricconversion element 111 is also charged until its electric potentialapproximately reaches the level of the electric potential of the sensorpower supply lines (VB1 to VBx).

This proves that the electric potential of the n-channel terminal of thephotoelectric conversion element 111 which is read upon application ofthe resetting signal to the sensor resetting transistor 114 is almostthe same as the electric potential of the photoelectric conversionelement 111 read after a black calibration sheet is read.

The description above is of an active CMOS sensor semiconductor device.Referring to FIG. 19, a passive CMOS sensor semiconductor device isdescribed below.

In the case of a passive semiconductor device, electric chargesaccumulated in the photoelectric conversion element 111 are read uponapplication of a selecting signal as shown in FIG. 19. Then thephotoelectric conversion element 111 is immediately charged until itselectric potential reaches the level of the electric potential of thesensor power supply lines (VB1 to VBx).

In this embodiment, electric charges accumulated in the photoelectricconversion element 111 are read when the photoelectric conversionelement 111 is charged until its electric potential reaches the level ofthe electric potential of the sensor power supply lines (VB1 to VBx). Inorder to achieve this operation, application of one selecting signal isimmediately followed by application of another selecting signal so thatthe accumulation time is shortened. Thereafter, the electric potentialof the photoelectric conversion element 111 which is charged to reachthe level of the electric potential of the sensor power supply lines(VB1 to VBx) is read.

Alternatively, the electric potential of the photoelectric conversionelement 111 may be read when the photoelectric conversion element ischarged until its electric potential reaches the level of the electricpotential of the sensor power supply lines (VB1 to VBx) in a prolongedselecting signal application time. A signal of the photoelectricconversion element is thus read with a short accumulation time.

The descriptions given in this embodiment are about CMOS typesemiconductor devices. However, the present invention is applicable toevery semiconductor device that has an image sensor function, includinga CCD type semiconductor device.

The semiconductor device operation described in this embodimentcorresponds to Step 2 explained in Embodiment Modes in the presentspecification and illustrated in FIG. 2. This means that Step 1 forwhite calibration can be combined with this embodiment to determinewhether there is a defective pixel and specify the coordinate of thedefective pixel.

This embodiment may be combined freely with Embodiment Modes 1 through 3and Embodiments 1 through 4.

Embodiment 6

This embodiment describes with reference to FIGS. 18 and 19 the electricpotential of a photoelectric conversion element when reading a whitecalibration sheet. FIG. 18 is used to describe the electric potential ofa photoelectric conversion element in an active semiconductor device andthen FIG. 19 is used to describe the electric potential of aphotoelectric conversion element in a passive semiconductor device.

The descriptions given in this embodiment are about the electricpotential of a photoelectric conversion element 111 when theaccumulation time of the photoelectric conversion element 111 isprolonged and the semiconductor device reads a white calibration sheet.

First, a specific description is given on the length of accumulationtime of the photoelectric conversion element 111 to which the presentinvention is applied.

A dark current flowing in the photoelectric conversion element 111 isdenoted by Id. The dark current Id is a current that flows in thephotoelectric conversion element 111 even when the photoelectricconversion element 111 is not irradiated with light. The capacitance ofthe photoelectric conversion element 111 is given as C, and theaccumulation time of the photoelectric conversion element 111 when thecapacitance thereof is C is given as T. The voltage applied to both endsof the photoelectric conversion element upon application of a resettingsignal is given as Vp. Then the amount of electric charges is given as Qand satisfies the following Expressions 4 and 5.

Expression 4

Q=C×Vp  (4)

Expression 5

Q=Id×T  (5)

The following Expression 6 is obtained from Expressions 4 and 5.

Expression 6

T=(C×Vp)/Id  (6)

In this embodiment, the electric potential of the n-channel terminal ofthe photoelectric conversion element 111 is read when the accumulationtime satisfies the following Expression 7.

Expression 7

T>(C×Vp)/Id  (7)

The electric potential of the n-channel terminal of the photoelectricconversion element 111 which is read with the accumulation timesatisfying Expression 7 is almost the same as the electric potential ofthe photoelectric conversion element 111 read after a white calibrationsheet is read. In other words, the operation of reading the electricpotential of the n-channel terminal of the photoelectric conversionelement 111 when the accumulation time satisfies Expression 7 is equalto the operation of reading a white calibration sheet. The reason isgiven below.

When a white calibration sheet is read, the photoelectric conversionelement 111 is irradiated with very bright light. In other words,photoelectric conversion nearing saturation takes place in thephotoelectric conversion element 111 and electric charges areaccumulated in the photoelectric conversion element 111. Therefore, theelectric potential of the n-channel terminal of the photoelectricconversion element 111 is discharged almost completely when reading awhite calibration sheet.

With the accumulation time satisfying Expression 7, the electricpotential of the n-channel terminal of the photoelectric conversionelement 111 is discharged almost completely and therefore the operationof reading the electric potential of the n-channel terminal of thephotoelectric conversion element 111 is equal to the operation ofreading a white calibration sheet.

This embodiment is effective for active semiconductor devices andpassive semiconductor devices both. The embodiment is also effective forCCD type semiconductor devices.

The driving method of this embodiment corresponds to Step 1 explained inEmbodiment Modes in the present specification and illustrated in FIG. 2.This means that Step 2 for black calibration can be combined with thisembodiment to determine whether there is a defective pixel and specifythe coordinate of the defective pixel.

This embodiment may be combined freely with Embodiment Modes 1 through 3and Embodiments 1 through 5.

Embodiment 7

This embodiment deals with subject's images actually obtained by usingthe present invention, and an image of a window of a system according tothe present invention. The system in this embodiment is made usingVisual Basic ver. 6.0 (Microsoft) installed in a Windows 98 personalcomputer.

FIG. 9 shows an image obtained after white calibration. As shown in FIG.9, defective pixels are displayed as black dots after white calibrationis conducted. FIG. 10 shows an image obtained after black calibration.As shown in FIG. 10, defective pixels are displayed as white dots afterblack calibration is conducted. The defective pixels are specified fromFIGS. 9 and 10.

FIG. 11 shows a display screen of the personal computer when the systemof the present invention is in operation. On the display screen of FIG.11, the image obtained by white calibration and shown in FIG. 9 isdisplayed as well as a table in which image signals of the image areexpressed as numbers. Also displayed on the screen are the imageobtained by black calibration and shown in FIG. 10 and a table in whichimage signals of the image are expressed as numbers.

FIG. 12 shows an image of a subject read by a semiconductor device towhich the present invention is not applied. FIG. 13 shows an image ofthe subject read by a semiconductor device to which the presentinvention is applied.

A comparison is made between FIGS. 12 and 13. In FIG. 12, defectivepixels are displayed as black dots and white dots. In FIG. 13, on theother hand, defective pixels are inconspicuous and seem as if they arerepaired because image signals of defective pixels are set based onimage signals of pixels surrounding the defective pixels.

This embodiment may be combined freely with Embodiment Modes 1 through 3and Embodiments 1 through 6.

Embodiment 8

Examples of electronic equipment using a semiconductor device of thepresent invention are described with reference to FIGS. 14A to 14D.

FIG. 14A shows a hand scanner using a line sensor. An optical system1002 such as a rod lens array is provided above a CCD type (CMOS type)image sensor 1001. The optical system 1002 is used to project an imageof a subject 1004 onto the image sensor 1001.

A light source 1003 such as an LED or fluorescent is positioned so as toirradiate the subject 1004 with light. Glass 1005 is placed under thesubject 1004.

Light emitted from the light source 1003 enters the subject 1004 throughthe glass 1005. The light reflected by the subject 1004 enters theoptical system 1002 through the glass 1005. After entering the opticalsystem 1002, the light enters the image sensor 1001 to be subjected tophotoelectric conversion in there.

In FIG. 14B, 1801 denotes a substrate; 1802, a pixel portion; 1803, atouch panel; and 1804, a touch pen. The touch panel 1803 islight-transmissive and transmits light emitted from the pixel portion1802 as well as light entering the pixel portion 1802. The device thuscan read an image of a subject through the touch panel 1803. An image onthe pixel portion 1802 can be seen through the touch panel 1803 whilethe pixel portion 1802 is displaying an image.

When the touch pen 1804 comes into contact with the touch panel 1803,the positional information of the point where the touch pen 1804 is incontact with the touch panel 1803 can be sent as an electric signal tothe semiconductor device. Any known touch panel and touch pen may beused as the touch panel 1803 and the touch pen 1804 of this embodimentas long as the touch panel is light-transmissive and the positionalinformation of the point where the touch pen is in contact with thetouch panel is sent as an electric signal to the semiconductor device.

The semiconductor device structured as above in accordance with thepresent invention reads information of an image to display the readimage in the pixel portion 1802, and allows a user to write or draw onthe displayed image with the touch pen 1804. In the semiconductor deviceof the present invention, the pixel portion 1802 handles all of readingan image, displaying the image, and writing or drawing on the image.Accordingly, it is possible for the semiconductor device to reduce itssize and have various functions.

FIG. 14C shows a portable hand scanner different from the one in FIG.14B. The scanner in FIG. 14C is composed of a main body 1901, a pixelportion 1902, a top cover 1903, an external connection port 1904, andoperation switches 1905. FIG. 14D shows the same portable hand scanneras the one in FIG. 14C with the top cover 1903 closed.

The semiconductor device of the present invention can displayinformation of a read image in the pixel portion 1902 to allow a user toimmediately confirm the image read without adding a display to thesemiconductor device.

An image signal read by the pixel portion 1902 may be sent to electronicequipment externally connected to the portable hand scanner through theexternal connection port 1904. Then the data can be processed in apersonal computer to correct, synthesize, or edit the image.

This embodiment may be combined freely with Embodiment Modes 1 through 3and Embodiments 1 through 7.

Embodiment 9

Given as examples of electronic equipment using a semiconductor deviceof the present invention are a video camera, a digital still camera, anotebook computer, and a portable information terminal (such as a mobilecomputer, a cellular phone, a portable game machine, or an electronicbook).

FIG. 15A shows a video camera, which is composed of a main body 2101, adisplay unit 2102, an image receiving unit 2103, an external connectionport 2105, operation keys 2104, a shutter 2106, etc. The presentinvention can be applied to the display unit 2102.

FIG. 15B shows a mobile computer, which is composed of a main body 2301,a display unit 2302, a switch 2303, operation keys 2304, an infraredport 2305, etc. The present invention can be applied to the display unit2302.

FIG. 15C shows a cellular phone, which is composed of a main body 2701,a case 2702, a display unit 2703, an audio input unit 2704, an audiooutput unit 2705, operation keys 2706, an external connection port 2707,an antenna 2708, etc. The present invention can be applied to thedisplay unit 2703.

As described above, the present invention has so wide an applicationrange that it is applicable to electronic equipment of any field.

This embodiment may be combined freely with Embodiment Modes 1 through 3and Embodiments 1 through 8.

With the defective pixel specifying method of the present invention, itis easy to determine whether there is a defective pixel and specify thecoordinate of the defective pixel. Furthermore, an image signal of thedefective pixel can readily be set by using the image correcting methodof the present invention. As a result, the defective pixel seems as ifit is repaired. The present invention gives a semiconductor devicehaving a defective pixel the same level of image sensor function asexhibited by a semiconductor device that has no defective pixel.Therefore the invention can improve the product yield.

1. A driving method of a device comprising a pixel portion, wherein thepixel portion includes a display element and a photoelectric conversionelement, the method comprising: obtaining a first signal by the pixelportion; obtaining a second signal by the pixel portion; obtaining athird signal by the pixel portion; correcting the third signal using thefirst signal and the second signal; and displaying an image on the pixelportion wherein the first signal is almost the same as a signal obtainedby reading a black calibration sheet, and the second signal is almostthe same as a signal obtained by reading a white calibration sheet. 2.The driving method according to claim 1, wherein the first signal isobtained by reading a black sheet which is placed over the pixelportion.
 3. The driving method according to claim 1, wherein the secondsignal is obtained by reading a white sheet which is placed over thepixel portion.
 4. The driving method according to claim 1, wherein thethird signal is obtained by reading an object over the pixel portion. 5.The driving method according to claim 1, wherein, in the step ofobtaining the first signal, a potential of the photoelectric conversionelement is read upon an application of a reset signal.
 6. The drivingmethod according to claim 1, wherein, in the step of obtaining the firstsignal, an accumulation time is short.
 7. A driving method of a devicecomprising a pixel portion, wherein the pixel portion includes a displayelement and a photoelectric conversion element, the method comprising:obtaining a first signal by the pixel portion; obtaining a second signalby the pixel portion; obtaining a first image by the pixel portion;correcting the first image using the first signal and the second signalto form a second image; and displaying the second image on the pixelportion wherein the first signal is almost the same as a signal obtainedby reading a black calibration sheet, and the second signal is almostthe same as a signal obtained by reading a white calibration sheet. 8.The driving method according to claim 7, wherein the first signal isobtained by reading a black sheet which is placed over the pixelportion.
 9. The driving method according to claim 7, wherein the secondsignal is obtained by reading a white sheet which is placed over thepixel portion.
 10. The driving method according to claim 7, wherein thefirst image is obtained by reading an object over the pixel portion. 11.The driving method according to claim 7, wherein, in the step ofobtaining the first signal, a potential of the photoelectric conversionelement is read upon an application of a reset signal.
 12. The drivingmethod according to claim 7, wherein, in the step of obtaining the firstsignal, an accumulation time is short.
 13. A driving method of a devicecomprising a pixel, wherein the pixel includes a display element, aphotoelectric conversion element and a transistor, and an n-channelterminal of the photoelectric conversion element is electricallyconnected to a gate of the transistor, the method comprising: obtaininga first potential of the n-channel terminal; obtaining a secondpotential of the n-channel terminal; obtaining a third potential of then-channel terminal; correcting the third potential using the firstpotential and the second potential; and applying a fourth potential tothe display element wherein the first potential is almost the same as apotential obtained by reading a black calibration sheet, and the secondpotential is almost the same as a potential obtained by reading a whitecalibration sheet.
 14. The driving method according to claim 13, whereinthe first potential is obtained by reading a black sheet which is placedover the pixel.
 15. The driving method according to claim 13, whereinthe second potential is obtained by reading a white sheet which isplaced over the pixel.
 16. The driving method according to claim 13,wherein the third potential is obtained by reading an object over thepixel.
 17. The driving method according to claim 13, wherein, the firstpotential is read upon an application of a reset signal.
 18. The drivingmethod according to claim 13, wherein, in the step of obtaining thefirst potential, an accumulation time is short.